复合盐侵蚀衬砌喷射混凝土耐久性退化研究

我国西部地区土壤及地下水中含有高浓度、及Cl，与隧道衬砌喷射混凝土发生一系列物理化学反应，造成其结构耐久性能退化。为系统研究复合盐侵蚀喷射混凝土耐久性能退化规律及机理，分别以10%Na2SO4溶液和5%Na2SO45%MgSO43.5%NaCl混合溶液为侵蚀介质，采用干湿交替法，开展喷射混凝土耐久性试验。、及Cl与氢氧化钙和铝相反应生成水镁石、石膏和Friedel盐，延缓钙矾石形成。复合盐侵蚀喷射混凝土物理力学性能退化速度明显小于硫酸盐侵蚀。硫酸盐侵蚀喷射混凝土以表面水泥砂浆和骨料的剥落为主，复合盐侵蚀主要以表面龟裂最终断裂为主，且裂缝中充满白色结晶盐。分析侵蚀喷射混凝土矿物组成和微观结构，硫酸盐侵蚀喷射混凝土产物主要为钙矾石和石膏，而复合盐侵蚀喷射混凝土产物组成复杂，包括碳硫硅钙石、水镁石、石膏、钙矾石、水化硅酸镁和结晶盐。硫酸盐侵蚀喷射混凝土中含量高于复合盐侵蚀，而混凝土pH值低。

Durability degradation of lining shotcrete exposed to compound salt

Salt lake is widely distributed in Western China. The high concentrations of , , and Cl in the soil and underground water are the major reasons leading to the performance degradation of lining shotcrete. In order to study the durability degradation and corrosion mechanism of lining shotcrete exposed to compound salt, the durability experiment is carried out in the solution of 10% Na2SO4 and the mixed solution of 5%Na2SO4-5%MgSO4-3.5%NaCl using the dry-wet (D&W) cyclic method. Physical and mechanical property degradation rate of shotcrete exposed to compound salt is slower than that of shotcrete exposed to sulfate, due to , , and Cl reacting with portlandite and aluminum phase which can form brucite, gypsum and Friedel’s salt. The destruction form of shotcrete exposed to sulfate appears to be peeling off of surface cement mortar and aggregate, while the one of shotcrete exposed to compound salt appears to be net-like microcracks on the surface and eventually appears to be fractured. Based on analysis of the mineral composition and microstructure of corroded shotcrete, it is found that ettringite and gypsum are the main product of sulfate corroded shotcrete. However, the products of compound salt corroded shotcrete are complicated and mainly include thaumasite, brucite, gypsum, ettringite, magnesium silicate and crystal salt. Sulfate ion content of shotcrete exposed to sulfate is higher than that of shotcrete exposed to compound salt, but pH value is lower.